Novel anti-cancer therapies increasingly involve targeting of the molecular-genetic abnormalities that result in oncogenesis. However, response to such therapies is often associated with tumor stasis, rather than shrinkage, limiting the utility of conventional imaging methods to monitor early response. Our long-term goal is to develop noninvasive, localized, magnetic resonance (MR)-based methods that detect molecular response to targeted treatments. We have shown that inhibition of signaling via the mitogen activated protein kinase (MAPK) and phosphatidylinositol 3-kinase (PI3K) pathways results in modulation of MR spectroscopy (MRS)-detectable choline-containing metabolites and in particular phosphocholine (PC). However, our data show that, depending on treatment, inhibition can result either in an increase or in a decrease in PC, limiting its use as a robust biomarker of response. The goal of this application is therefore to determine the mechanisms by which signaling pathways affect cellular metabolism resulting in modulation of PC and other choline-containing metabolites. A secondary goal is to identify and validate biomarkers of response to previously unexplored targeted therapies. This pre-clinical research will result in a better understanding of the mechanisms that lead to changes in choline-containing metabolites. As a result, it will be possible to use the modulation in these metabolites in a more reliable, robust and predictable way to assess response to therapies that target signaling. MAPK and PI3K signaling can affect choline-containing metabolites either directly, by affecting the enzymes involved in choline metabolism, or indirectly, by affecting fatty acid synthase (FASN), which controls fatty acid (FA) synthesis. Thus, we propose to investigate both choline metabolism and fatty acid synthesis. We will combine 1H, 31P and 13C MRS and monitor how modulation of signaling affects the two metabolic pathways, and, consequently, choline-containing metabolites. Specific Aim 1. To determine the effect of fatty acid synthesis on choline metabolism. We will first determine how inhibition of FASN affects FA and choline metabolism. We will study live cells and extracts, and use 1H, 31P, 13C MRS to monitor metabolism. Specific Aim 2. To determine the mechanistic link between signaling pathways and metabolism. Using the same methods as above us will monitor the effect on FA and choline metabolism of 1) MAPK inhibition 2) PI3K inhibition and 3) inhibition of multiple signaling pathways via HSP90. Specific Aim 3. To confirm that the mechanistic findings in cells translate to tumors in vivo. Subcutaneous tumor xenografts will be investigated by 1H, 31P, 13C MRS to confirm that the findings made in Specific Aim 2 hold true in vivo. PUBLIC HEALTH RELEVANCE Magnetic resonance spectroscopy can be used to noninvasively monitor response to novel cancer therapies that target specific oncogenic mutations. However, the exact mechanism behind the magnetic resonance-detectable metabolic changes previously reported following treatment is not clear. In this application we will investigate this link, and our research will result in more robust, reliable, and predictable, noninvasive, magnetic resonance-based indicators of tumor response to treatment, ultimately improving patient care.